Unconditionally fully initialized variable errors with possibly uninitialized

[gnzlbg]

This works (Playground):

pub unsafe fn foo() -> u32 {
    let r: u32;
    asm!("cpuid\n"
             : "={eax}"(r)
             : "{eax}"(0), "{ecx}"(0)
             : "rbx" :);
    r
}

but this fails (Playground):

pub struct A { pub eax: u32 }
pub unsafe fn bar() -> A {
    let r: A;
    asm!("cpuid\n"
             : "={eax}"(r.eax)
             : "{eax}"(0), "{ecx}"(0)
             : "rbx" :);
    r
}

with

error[E0594]: cannot assign to field `r.eax` of immutable binding
 --> src/lib.rs:7:25
  |
5 |     let r: A;
  |         - help: make this binding mutable: `mut r`
6 |     asm!("cpuid\n"
7 |              : "={eax}"(r.eax)
  |                         ^^^^^ cannot mutably borrow field of immutable binding

error[E0381]: use of possibly uninitialized variable: `r`
  --> src/lib.rs:10:5
   |
10 |     r
   |     ^ use of possibly uninitialized `r`

In particular, making r mut (Playground):

pub struct A { pub eax: u32 }
pub unsafe fn bar() -> A {
    let mut r: A;
    asm!("cpuid\n"
             : "={eax}"(r.eax)
             : "{eax}"(0), "{ecx}"(0)
             : "rbx" :);
    r
}

still errors with:

error[E0381]: use of possibly uninitialized variable: `r`
  --> src/lib.rs:10:5
   |
10 |     r
   |     ^ use of possibly uninitialized `r`

even though r is fully initialized. However this works (Playground):

pub struct A { pub eax: u32 }
pub unsafe fn bar() -> A {
    let r: u32;
    asm!("cpuid\n"
             : "={eax}"(r)
             : "{eax}"(0), "{ecx}"(0)
             : "rbx" :);
    A{ eax: r }
}

I expected that all of these would either work, or not work. They all look the same to me.

[hanna-kruppe]

See #54987

[gnzlbg]

This is indeed a duplicate of #54987 .